The present invention relates to the field of spinal implants, in particular for arthrodesis of at least two vertebral structures. The present invention more particularly relates to a system of spinal implants intended to ensure fusion of at least two adjacent vertebrae (i.e. arthrodesis).
A problem in the field of implants relates to bone growth and notably arthrodesis, i.e. the bone fusion of two structures, such as for example vertebrae. Indeed, sometimes a fusion of at least two vertebrae is sought to be obtained, for example when at least one of their adjacent intervertebral discs is lesioned. From the prior art various arthrodesis techniques are known, based on diverse types of implants, such as for example intersomatic (or arthrodesis) cages inserted in the place of a disc for promoting bone growth, or arthrodesis plate attached on two vertebrae for immobilizing them and allowing arthrodesis, or further osteosynthesis or arthrodesis bars, used for immobilizing the vertebrae, to which they are generally connected by pedicular screws or hooks, or finally interspinous implants inserted between the spines of the vertebrae (or “spinous processes”) for immobilizing them and thus facilitating fusion. The bars or plates are generally used as an addition to intersomatic cages which allow extended fusion since it is located at the vertebral bodies. This additional use results from a problem known in the field which is to stabilize the vertebral level to be treated. It is also known, notably at the lumbar and sacral level, of solutions using facet implants (interfacet or transfacet implants) allowing attachment of the articular facets with the purpose of obtaining fusion.
Generally, these solutions aim at further solving the problem of the stability of the implant and of the treated vertebral structures. It is necessary that an implant be stable in its implantation site, in particular when arthrodesis is desired since the latter should take place in a relative position of the rachis elements which is optimum (as desired by the surgeon). Stabilization and/or a locking of the implant are therefore often preferable. Various solutions of the prior art therefore aim at providing stable arthrodesis implants.
Thus, it has been suggested in the prior art that it would be desirable to use implants which are complementary with each other, such as for example osteosynthesis bars or plates in combination with intersomatic cages. Further, the fact that the rachis has actually three major stability axes has been suggested in the literature, notably by F. Denis in his/her article “The Three Column Spine and Its Significance in the Classification of Acute Thoracolumbar Spinal Injuries” in the journal SPINE 1983. Vol. 8, no. 8, pp 817-831, but also by R. Louis in his/her article “Spinal stability as defined by the three-column spine concept” in the journal Anatomia Clinica, 1985 Vol. 7, pp 33-42, and then by R. Roy-Camille in his/her article “L'instabilité Rachidienne/Spinal Instability” in the journal Rachis, 1994, Vol. 6, no. 2 pp 107-112 and more recently by Sabina MARCOVSCHI CHAMPAIN, in her thesis for obtaining the Doctoral degree of the l'École Nationale Supérieure d'Arts et Métiers, specialization “Biomechanics” at the l'École doctorale no. 432 (Sciences des Métiers de l'Ingénieur), document no. 2008/ENAM-0024.
However, most solutions of the prior art do not give the possibility of benefiting from these teachings of the literature and of proposing a stable spinal arthrodesis system, notably because of the general problems of the ease and/or rapidity of the implantation and of the invasivity of the implants and of surgical techniques which depend thereon. Indeed, it is generally desired that the implants be able to be rapidly and/or easily implanted with minimum invasivity, i.e. it is sought to limit the size of the incisions and damages on the surrounding tissues. This invasivity problem in particular relates to the introduction of the implants into the spine and notably the access to the intervertebral spaces (disc spaces) which is often particularly delicate because of the congestion, for example because of the presence of blood vessels and nerves near the intervertebral space, as well of the proximity of the spinal cord. The implants and their bone anchoring devices have to penetrate sufficiently deeply into the vertebrae for ensuring good attachment. As regards the implantation, various approach routes for placing the implant are possible, even if a given route is generally preferred for each of the various spinal stages, sometimes because of the preference and facility of the surgeon for this route, but also because of the pathology to be treated (a hernia may be rather posterior, therefore easier to withdraw through a posterior route), but further because of the anatomy of the patient (vessels in the axis of the anterior approach route or too prominent muscles, etc). For example (in a non-limiting way), a median anterior mini-invasive approach (MIS, “Mini-Invasive Spine Surgery”) approach may be preferred for cervical vertebrae and a lateral or anterolateral mini-invasive approach for thoracic or lumbar vertebrae. In particular, certain implants (notably intersomatic cages), generally at the lumbar level are provided so as to be implanted through a posterior route (from the rear of the patient) or a transforaminal route (through the foramen). The posterior route generally requires resection (generally partial resection) of the articular and/or facets and passes between the dura mater and the articulars (generally two cages are provided each positioned on one side of the sagittal plane). This route therefore follows a path very close to the spinal cord. The transforaminal route follows an oblique route relatively to the sagittal plane and requires cages with a sufficient length so as to be positioned obliquely or perpendicularly to the sagittal plane. Access routes as small as possible are generally sought in order to limit invasivity of the implantation surgical operation. Thus, in order to obtain an implant as less invasive as possible (i.e., not requiring the clearing of a wide approach route), it is necessary to reduce the size of the implant and ideally to limit the size of the passage required both for implantation and for attachment of the implant. Indeed, the implants which are anchored in vertebrae often add an additional constraint on the size and invasivity.
It will be noted that the invasivity problem provides additional constraints for meeting the stability problem, notably because the fact of reducing the dimensions for reducing the invasivity is accompanied with risks of instability. It is therefore interesting to propose a solution which allows reconciliation of the constraints related to invasivity and stability.
In this context, it is interesting to propose a solution giving the possibility of effectively tackling at least one portion of these problems.